The present invention relates to a cylindrical base body for a photosensitive drum used for an electrophotographic apparatus and an electrostatic recording apparatus, a photosensitive drum using the base body, and a method of producing the base body.
In an electrostatic recording process using a copying machine, a facsimile, a printer, and the like, the printing is performed by uniformly electrostatically charging the surface of a photosensitive drum; projecting an image from an optical system on the surface of the photosensitive drum, to erase the charges on a portion, on which light has impinged, of the surface of the photosensitive drum, thereby forming an electrostatic latent image thereon; supplying toner to the electrostatic latent image, to form a toner image by electrostatic adhesion of the toner thereon, and transferring the toner image to a recording medium such as paper, OHP sheets (transparency), and photographic paper.
As the photosensitive drum used for such an electrostatic recording process, a photosensitive drum having a structure shown in FIG. 1 has been generally used.
The photosensitive drum is configured such that flanges 2a and 2b are fixedly fitted to both ends of a cylindrical base body 1 having good conductivity, and a photosensitive layer 3 is formed on the outer peripheral surface of the cylindrical base body 1. In general, as shown in FIG. 1, two supporting shafts 4 provided on a main body “a” of an electrophotographic apparatus are inserted in two shaft holes 5 provided in both the flanges 2a and 2b, and a drive gear 6 formed on one flange 2b is meshed with a gear 7 connected to a motor or the like as a drive source, whereby the photosensitive drum is rotatably supported by the main body “a” of the electrophotographic apparatus.
The cylindrical base body 1 has been made from an aluminum alloy being in relatively lightweight and being good in machinability and conductivity.
The cylindrical base body made from an aluminum alloy must be highly accurately machined in order to satisfy requirements for strict dimensional accuracy and specific surface roughness. Also, portions in which the flanges 2a and 2b are to be fixedly fitted must be formed in both the ends of the cylindrical base body by machining. Further, the cylindrical base body must be subjected to a surface treatment for preventing oxidation or the like, as needed. This presents a problem in increasing the number of production steps, thereby raising the production cost. In this way, an aluminum alloy is not necessarily suitable as the material for forming the cylindrical base body of a photosensitive drum.
On the other hand, there has been known a photosensitive drum using a resin pipe as the cylindrical base body 1. The resin pipe is formed by injection-molding a conductive resin composition containing a thermoplastic resin and a conductive agent such as carbon dispersed therein. In this case, as described above, the outer peripheral surface of the cylindrical base body 1 is coated with the photosensitive layer 3. In the case of using such a resin made base body, at least one of the flanges 2a and 2b is made from a resin in such a manner as to be integrated with the resin made base body 1, and further, the drive gear 6 is also formed integrally with the flange integrated with the base body 1.
The photosensitive drum using the resin made base body is advantageous in omitting a number of machining steps, which has been required in the case of using the base body made from an aluminum alloy, and in reducing the weight of the photosensitive drum. Further, by integrating the flange and drive gear with the base body, it is possible to significantly stabilize conduction between the flange and drive gear and the base body.
The photosensitive drum using the resin made base body, however, may often fail to obtain a good image quality, and is expected to be improved in terms of such a point.
On the other hand, in the case of producing a photosensitive drum by forming the photosensitive layer 3 on the base body 1 as shown in FIG. 1, an under coat layer (not shown in FIG. 1) is generally formed between the base body 1 and the photosensitive layer 3.
The under coat layer serves as a primer for enhancing adhesiveness of the photosensitive layer, and as a insulating layer for covering microscopic abnormality (burrs and damages) on the surface of the base body so as to keep good electric performance. The under coat layer is generally configured as an insulating layer made from an amorphous copolymer nylon mainly containing nylon 12. Such an under coat layer is generally provided not only for the base body made from aluminum but also for the base body made from a conductive resin.
The formation of the under coat layer, however, requires a resin coating step, and from the viewpoint of cost reduction, it is expected to omit the formation of such an under coat layer.